June 13 (Reuters) - Salmonella has been found in a health food powder, spurring product recalls in the United States and the launch of a multistate health investigation, federal officials said on Friday.

Chia seed powder, commonly used in smoothies and snacks for its nutritional value, has sickened at least 21 people across the United States.

"It is the first time that chia powder has been identified as a food that transmits salmonella," said Centers for Disease Control and Prevention investigator Dr. Laura Gieraltowski.

Salmonella, the most common foodborne illness usually found in meat and egg products, sickens about 1.2 million people in the United States and results in 450 deaths each year, according to the CDC.

The number of chia-linked salmonella outbreaks is extremely low compared with illnesses caused by other foods. However, the powder's long shelf life and small serving size could mean that more people are getting ill but do not realize it, Gieraltowski said.

"People are just getting sick at a slower rate," Gieraltowski said.

Last month, state and federal officials began investigating 11 reports of salmonella outbreaks across the United States that were eventually traced back to chia powder. Investigators identified two new strains of salmonella in the powder, named Hartford and Newport.

Many of those sickened reported having vegan, vegetarian or largely organic diets, Gieraltowski said. They had a median age of 49.

Chia powder, made from finely ground, sprouted chia seeds rich in omega-3 fatty acids, has been made popular, in part, by a demand for gluten-free and health food products.

While it is unknown how salmonella is transmitted trough chia seeds, sprouted seeds have been known to conduct salmonella and E. coli, she said.

Some 34 additional infections tied to chia powder foods were recently reported in Canada, the CDC said in a statement.